A motor device using a motor keeps driving the motor according to a detection signal acquired from a rotation position sensor of the motor. On the other hand, when a detection signal has an abnormality, the motor device notifies the abnormality state to a user, thereby achieving a safe operation of the motor through rapid maintenance. Patent Literature 1 describes therein a technique for determining whether detection signals of two rotation position sensors match with an amplitude during normal time, and detecting an abnormality of the rotation position sensors based on the determination result. Patent Literature 2 describes therein a technique for, when an abnormality is detected in an output signal of any one of three-phase output rotation position sensors, keeping driving the motor by use of the two remaining output signals.